Assessing osseointegration of metallic implants with boronized surface treatment.

BACKGROUND: Modification of endosteal implants through surface treatments have been investigated to improve osseointegration. Boronization has demonstrated favorable mechanical properties, but limited studies have assessed translational, in vivo outcomes. This study investigated the effect of implant surface boronization on bone healing. MATERIAL AND METHODS: Two implant surface roughness profiles (acid etched, machined) in CP titanium (type II) alloy implants were boronized by solid-state diffusion until 10-15µm boron coating was achieved. The surface-treated implants were placed bilaterally into 5 adult sheep ilia for three and six weeks. Four implant groups were tested: boronized machined (BM), boronized acid-etched (BAA), control machined (CM), and control acid-etched (CAA). Osseointegration was quantified by calculating bone to implant contact (BIC) and bone area fraction occupancy (BAFO). RESULTS: Both implant types treated with boronization had BIC values not statistically different from machined control implants at t=3 weeks, and significantly less than acid-etched control (p<0.02). BAFO values were not statistically different for all 3-week groups except machined control (significantly less at p <0.02). BAFO had a significant downward trend from 3 to 6 weeks in both boronized implant types (p<0.03) while both control implant types had significant increases in BIC and BAFO from 3 to 6 weeks. CONCLUSIONS: Non-decalcified histology depicted intramembranous-like healing/remodeling in bone for controls, but an absence of this dynamic process in bone for boronized implants. These findings are inconsistent with in vitro work describing bone regenerative properties of elemental Boron and suggests that effects of boron on in vivo bone healing warrant further investigation.

Osteogenic parameters surrounding trabecular tantalum metal implants in osteotomies prepared via osseodensification drilling.

BACKGROUND: Surgical fixation of implants into bone for the correction of bone deformities or defects is a traditional approach for skeletal stabilization. Important measures of efficacy of implants include implant stability and osseointegration-the direct interaction between living bone and an implant. Osseointegration depends on successful implant placement and subsequent bone remodeling. This study utilized osseodensification drilling (OD) in a low bone density model using trabecular metal (TM) implants. MATERIAL AND METHODS: Three osteotomy sites, Regular, OD-CW (clockwise), and OD-CCW (counterclockwise), were prepared in each ilium of three female sheep. Drilling was performed at 1100rpm with saline irrigation. Trabecular metal (TM) (Zimmer, Parsippany, NJ, USA) implants measuring 3.7mm in diameter x 10mm length were placed into respective osteotomies. A three-week period post-surgery was given to allow for healing to take place after which all three sheep were euthanized and the ilia were collected. Samples were prepared, qualitatively and quantitatively analyzed using histology micrographs and image analysis software (ImageJ, NIH, Bethesda, MD). Bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) were quantified to evaluate the osseointegration parameters. RESULTS: All implants exhibit successful bone formation in the peri-implant environment as well as within the open spaces of the trabecular network. Osseointegration within the TM (quantified by %BIC) as a function of drilling technique was more pronounced in OD samples(p>0.05). The %BAFO however shows a significant difference (p=0.036) between the CCW and R samples. Greater bone volume and frequency of bone chips are observed in OD samples. CONCLUSION: The utilization of OD as a design for improved fixation of hardware was supported by increased levels of stability, both primary and secondary. Histological data with OD provided notably different results from those of the regular drilling method.

Unusual topogenic sequence directs prion protein biogenesis.

Biosynthetic studies of the prion protein (PrP) have shown that two forms of different topology can be generated from the same pool of nascent chains in cell-free translation systems supplemented with microsomal membranes. A transmembrane form is the predominant product generated in wheat germ (WG) extracts, whereas a completely translocated (secretory) form is the major product synthesized in rabbit reticulocyte lysates (RRL). An unusual topogenic sequence within PrP is now shown to direct this system-dependent difference. The actions of this topogenic sequence were independent of on-going translation and could be conferred to heterologous proteins by the engineering of a discrete set of codons. System-dependent topology conferred by addition of RRL to WG translation products suggests that this sequence interacts with one or more cytosolic factors.

Total penile reconstruction: A systematic review.

BACKGROUND: Phalloplasty poses a unique challenge to the plastic and reconstructive surgeon. The development of advanced microsurgical techniques has greatly augmented the range of surgical approaches available. METHODS: A systematic review of the MEDLINE and Cochrane databases was performed to identify clinical studies of total penile reconstruction published within the last 10 years using the search algorithm: "(phallus or penis or penile) and (reconstruction or phalloplasty or transplant)". RESULTS: The primary literature search retrieved 1400 articles. After applying inclusion and exclusion criteria, 30 studies were selected for review. The radial forearm free flap is the preferred technique for total phalloplasty; however, other techniques including the fibular osteocutaneous flap, anterolateral thigh flap, latissimus dorsi flap, scapular free flap, and abdominal flap are described. Background, indications, and preoperative and postoperative care are also discussed. CONCLUSIONS: Total penile reconstruction can provide functional, aesthetic, and psychosocial benefits to the patient. Use of the radial forearm free flap has been proposed as the gold standard; however, the wide range of potential complications associated with phalloplasty warrants an individualized approach to each patient.

Proapoptotic p53-interacting protein 53BP2 is induced by UV irradiation but suppressed by p53.

p53 is an important mediator of the cellular stress response with roles in cell cycle control, DNA repair, and apoptosis. 53BP2, a p53-interacting protein, enhances p53 transactivation, impedes cell cycle progression, and promotes apoptosis through unknown mechanisms. We now demonstrate that endogenous 53BP2 levels increase following UV irradiation induced DNA damage in a p53-independent manner. In contrast, we found that the presence of a wild-type (but not mutant) p53 gene suppressed 53BP2 steady-state levels in cell lines with defined p53 genotypes. Likewise, expression of a tetracycline-regulated wild-type p53 cDNA in p53-null fibroblasts caused a reduction in 53BP2 protein levels. However, 53BP2 levels were not reduced if the tetracycline-regulated p53 cDNA was expressed after UV damage in these cells. This suggests that UV damage activates cellular factors that can relieve the p53-mediated suppression of 53BP2 protein. To address the physiologic significance of 53BP2 induction, we utilized stable cell lines with a ponasterone A-regulated 53BP2 cDNA. Conditional expression of 53BP2 cDNA lowered the apoptotic threshold and decreased clonogenic survival following UV irradiation. Conversely, attenuation of endogenous 53BP2 induction with an antisense oligonucleotide resulted in enhanced clonogenic survival following UV irradiation. These results demonstrate that 53BP2 is a DNA damage-inducible protein that promotes DNA damage-induced apoptosis. Furthermore, 53BP2 expression is highly regulated and involves both p53-dependent and p53-independent mechanisms. Our data provide new insight into 53BP2 function and open new avenues for investigation into the cellular response to genotoxic stress.

Apoptosis-stimulating protein of p53-2 (ASPP2/53BP2L) is an E2F target gene.

The p53 pathway is a central apoptotic regulator. Deregulation of the Rb/E2F pathway occurs in a majority of tumors, resulting in both unrestrained proliferation and enhanced apoptosis sensitivity via p53-dependent and independent mechanisms. However, the mechanisms coupling the p53 and Rb/E2F pathways remain incompletely understood. We report that ASPP2/53BP2L, a p53/p73-binding protein that promotes p53/p73-dependent apoptosis, is an E2F target gene. The ASPP2/53BP2L promoter was identified and ectopic expression of transcription-competent E2F-1 (E2F-2 and E2F-3) stimulated an ASPP2/53BP2L promoter-luciferase reporter. Mutational analysis of the ASPP2/53BP2L promoter identified E2F-binding sites that cooperate for E2F-1 induction and basal repression of ASPP2/53BP2L. Moreover, endogenous ASPP2/53BP2L levels increased after E2F-1 expression, and E2F-1 bound the endogenous ASPP2/53BP2L promoter after chromatin immunoprecipitation. Typical for an E2F target, ASPP2/53BP2L expression was maximal in early S-phase. Thus, ASPP2/53BP2L is downstream of E2F, suggesting that it functions as a common link between the p53/p73 and Rb/E2F apoptotic pathways.

Non-hydrophobic extracytoplasmic determinant of stop transfer in the prion protein.

A universal feature of integral transmembrane proteins is a hydrophobic peptide segment that spans the lipid bilayer. These hydrophobic domains are important for terminating the translocation of the polypeptide chain across the membrane of the endoplasmic reticulum (a process termed stop transfer) and for integrating the protein into the bilayer. But a role for extracytoplasmic sequences in stop transfer and transmembrane integration has not previously been shown. Recently, a sequence which directs an unusual mode of stop transfer has been identified in the prion protein. This brain glycoprotein exists in two isoforms, which are identical both in primary amino-acid sequence and in containing phosphatidylinositol glycolipid linkages at their C termini, which can be cleaved by a phosphatidylinositol-specific phospholipase C9. But only one of the isoforms (PrPC) is released from cells on treatment with this phospholipase, indicating that the two isoforms have either different subcellular locations or transmembrane orientations. Consistent with this is the observation of two different topological forms in cell-free systems. An unusual topogenic sequence in the prion protein seems to direct these alternative topologies (manuscript in preparation). In the wheat-germ translation system, this sequence directs nascent chains to a transmembrane orientation; by contrast, in the rabbit reticulocyte lysate system, this sequence fails to cause stop transfer of most nascent chains. We have now investigated determinants in this unusual topogenic sequence that direct transmembrane topology, and have demonstrated that (1) a luminally disposed charged domain is required for stop transfer at the adjacent hydrophobic domain, (2) a precise spatial relationship between these domains is essential for efficient stop transfer, and (3) codons encompassing this hydrophilic extracytoplasmic domain confer transmembrane topology to a heterologous protein when engineered adjacent to the codons for a normally translocated hydrophobic domain. These results identify an unexpected functional domain for stop transfer in the prion protein and have implications for the mechanism of membrane protein biogenesis.